Optical film for improving contrast ratio, polarizing plate including same, and liquid crystal display device including same

ABSTRACT

An optical film for improving contrast ratio, a polarizing plate including the same, and a liquid crystal display including the same are disclosed. The optical film for improving contrast ratio includes: a base layer and a contrast ratio improvement layer formed on the base layer, wherein the contrast ratio improvement layer includes a high refractive index resin layer including a patterned portion composed of one or more engraved patterns and a flat portion formed between the engraved patterns and a low refractive index resin layer directly formed on the patterned portion, the engraved patterns have a base angle of 75° to about 90°, and the patterned portion has a P/W value of greater than about 1 to about 10 or less (P is the cycle of the patterned portion (unit: μm) and W is the maximum width of the engraved pattern (unit: μm)).

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a National Phase Patent Application and claimspriority to and the benefit of International Application NumberPCT/KR2016/004465, filed on Apr. 28, 2016, which claims priority toKorean Application No. 10-2016-0051816, filed on Apr. 27, 2016, andKorean Application No. 10-2015-0060935, filed on Apr. 29, 2015, theentire contents of all of which are incorporated herein by reference.

BACKGROUND 1. Field

The present invention relates to an optical film for improving contrastratio, a polarizing plate including the same, and a liquid crystaldisplay including the same.

2. Description of the Related Art

A liquid crystal display is operated to emit light through a liquidcrystal panel after receiving the light from a backlight unit. Thus, theliquid crystal display provides a good front contrast ratio (CR).However, the liquid crystal display has a lower contrast ratio at sideor lateral sides thereof than at front side. Various attempts have beenmade in order to increase side contrast ratio by modification of aliquid crystal panel or a liquid crystal structure. Higher side contrastratio causes deterioration in front contrast ratio. Accordingly, thereis a need for minimization of decrease of the front contrast ratio whileincreasing the side contrast ratio in order to improve visibility.

Decrease in side contrast ratio can be prevented by diffusing collectedlight having passed through a liquid crystal panel and a polarizingplate. Diffusion of the collected light can be achieved through anoptical film including beads. However, such an optical film can providelow diffusion efficiency or can be difficult to produce.

Recently, an inverted prism sheet including prisms formed on a lightincidence plane thereof is applied to a liquid crystal display. Theinverted prism sheet can provide higher brightness than a typical prismsheet including prisms formed on a light exit plane. However, a liquidcrystal display including such an inverted prism sheet is also requiredto increase relative brightness and contrast ratio in order to improveimage quality. Particularly, an optical film for improving contrastratio or a polarizing plate, which are capable of improving bothrelative brightness and contrast ratio for both the liquid crystaldisplay including the inverted prism sheet having prisms formed on thelight incidence plane thereof and the liquid crystal display includingthe prism sheet having prisms formed on the light exit plane thereof canbe very useful.

One example of the background technique is disclosed in Japanese PatentLaid-open Publication No. 2006-251659.

SUMMARY

It is one aspect of the present invention to provide an optical film forimproving contrast ratio, which can increase relative brightness,improve front contrast ratio and side contrast ratio, and minimize adecrease of the front contrast ratio while increasing the side contrastratio.

It is another aspect of the present invention to provide an optical filmfor improving contrast ratio, which can reduce a difference between thefront contrast ratio and the side contrast ratio.

It is other aspect of the present invention to provide an optical filmfor improving contrast ratio, which can increase contrast ratio at thesame side viewing angle and at the same front viewing angle.

It is other aspect of the present invention to provide an optical filmfor improving contrast ratio, which can improve image quality.

It is other aspect of the present invention to provide an optical filmfor improving contrast ratio, which can improve both relative brightnessand contrast ratio in each of a liquid crystal display including a prismsheet having prisms formed on a light incidence plane thereof and aliquid crystal display including a prism sheet having prisms formed on alight exit plane thereof.

It is other aspect of the present invention to provide an, which can aliquid crystal display, which includes a prism sheet having prismsformed on a light incidence plane thereof and has improved properties interms of front contrast ratio, side contrast ratio, side viewing angle,and brightness.

In accordance with one aspect of the present invention, an optical filmfor improving contrast ratio may include: a base layer and a contrastratio improvement layer formed on the base layer, wherein the contrastratio improvement layer includes a high refractive index resin layerincluding a patterned portion composed of one or more engraved patternsand a flat portion formed between the engraved patterns and a lowrefractive index resin layer directly formed on the patterned portion,the engraved patterns have a base angle of 75° to about 90°, and thepatterned portion has a P/W value of greater than about 1 to about 10 orless (P is the cycle of the patterned portion (unit: μm) and W is themaximum width of the engraved pattern (unit: μm)).

In accordance with another aspect of the present invention, a polarizingplate may include the optical film for improving contrast ratio as setforth in the present invention.

In accordance with a further aspect of the present invention, a liquidcrystal display may include the optical film for improving contrastratio as set forth in the present invention.

In accordance with yet another aspect of the present invention, a liquidcrystal display may include a light guide plate; a prism sheet; a firstpolarizing plate; a liquid crystal panel; and a second polarizing platesequentially stacked one above another, wherein the prism sheet includesone or more prisms formed on a surface thereof facing the light guideplate and the second polarizing plate includes the optical film forimproving contrast ratio as set forth in the present invention.

The present invention provide an optical film for improving contrastratio, which can improve relative brightness, front contrast ratio andside contrast ratio while minimizing decrease in front contrast ratio.

The present invention provide an optical film for improving contrastratio, which can reduce a difference between the front contrast ratioand the side contrast ratio.

The present invention provide an optical film for improving contrastratio, which can increase contrast ratio at the same side viewing angleand the same front viewing angle.

The present invention could provide an optical film for improvingcontrast ratio, which can improve image quality.

The present invention could provide an optical film for improvingcontrast ratio, which can improve both relative brightness and contrastratio in each of a liquid crystal display including a prism sheet havingprisms formed on a light incidence plane thereof and a liquid crystaldisplay including a prism sheet having prisms formed on a light exitplane thereof.

The present invention could provide a liquid crystal display, whichincludes a prism sheet having prisms formed on a light incidence planethereof and has improved properties in terms of front contrast ratio,side contrast ratio, side viewing angle, and brightness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an optical film for improvingcontrast ratio according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of an optical film for improvingcontrast ratio according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view of an optical film for improvingcontrast ratio according to a further embodiment of the presentinvention.

FIG. 4 is a cross-sectional view of an optical film for improvingcontrast ratio according to yet another embodiment of the presentinvention.

FIG. 5 is a cross-sectional view of a polarizing plate according to oneembodiment of the present invention.

FIG. 6 is a cross-sectional view of a polarizing plate according toanother embodiment of the present invention.

FIG. 7 is a cross-sectional view of a polarizing plate according to afurther embodiment of the present invention.

FIG. 8 is a cross-sectional view of a polarizing plate according to yetanother embodiment of the present invention.

FIG. 9 is a schematic perspective view of a liquid crystal displayaccording to one embodiment of the present invention.

FIG. 10 is a cross-sectional view of a prism sheet of the liquid crystaldisplay shown in FIG. 9.

FIG. 11 is a conceptual view of a light exit angle of the light guideplate.

DETAILED DESCRIPTION

Embodiments of the present invention will be described in detail withreference to the accompanying drawings to provide a thoroughunderstanding of the invention to those skilled in the art. It should beunderstood that the present invention may be embodied in different waysand is not limited to the following embodiments. In the drawings,portions irrelevant to the description will be omitted for clarity. Likecomponents will be denoted by like reference numerals throughout thespecification.

As used herein, spatially relative terms such as “upper” and “lower” aredefined with reference to the accompanying drawings. Thus, it will beunderstood that “upper” can be used interchangeably with “lower”,“lower” can be used interchangeably with “upper”. It will be understoodthat when a layer is referred to as being “on” another layer, it can bedirectly formed on the other layer, or intervening layer(s) may also bepresent. Thus, it will be understood that when a layer is referred to asbeing “directly on” another layer, no intervening layer is interposedtherebetween.

As used herein, the terms “horizontal direction” and “verticaldirection” mean a longitudinal direction and a transverse direction of arectangular screen of a liquid crystal display, respectively. As usedherein, the term “side surface” means a region in which θ ranges from60° to 90° in which a front side is indicated by (0°, 0°), a left endpoint is indicated by (180°, 90°), and a right end point is indicated by(0°, 90°) in a spherical coordinate system (Φ, θ) with reference to thehorizontal direction.

As used herein, the term “top part” refers to a portion located at anuppermost portion of an optical structure.

As used herein, the term “aspect ratio” refers to a ratio of maximumheight of an optical structure to maximum width thereof (maximumheight/maximum width).

As used herein, the term “cycle” means the distance between adjacentengraved patterns, for example, the sum of a width of one engravedpattern and a width of one flat portion.

As used herein, “in-plane retardation (Re)” is represented by EquationA:Re=(nx−ny)×d  <Equation A>

(In Equation A, wherein nx and ny are refractive indexes at a wavelengthof 550 nm in the slow axis direction and the fast axis direction of acorresponding optical element, respectively, and d is the thickness ofthe corresponding optical element (unit: nm)).

As used herein, the term “(meth)acryl” refers to acryl and/or methacryl.

As used herein, the term “radius of curvature” means, in the case of anoptical pattern having a curved surface at a top part thereof, a radiusof an imaginary circle including the curved surface or, in the case of aprism pattern, a radius of an imaginary circle including a curvedsurface tangential to both one inclined plane of the prism and the otherinclined plane of the prism meeting the one inclined plane.

Hereinafter, an optical film for improving contrast ratio according toone embodiment of the present invention will be described with referenceto FIG. 1. FIG. 1 is a cross-sectional view of an optical film forimproving contrast ratio according to one embodiment of the presentinvention.

Referring to FIG. 1, an optical film 10 for improving contrast ratioaccording to one embodiment may include a contrast ratio improvementlayer 100 and a base layer 200.

The contrast ratio improvement layer 100 includes a high refractiveindex resin layer 110, which includes a patterned portion composed ofone or more engraved patterns 111 and a flat potrion 112 formed betweenthe engraved patterns 111, and a low refractive index resin layer 120directly formed on the high refractive index resin layer 110. Herein,the expression “directly formed on” means that any intervening layerssuch as an adhesive layer, a bonding layer and/or other optical layersare not formed between the high refractive index resin layer 110 and thelow refractive index resin layer 120. As such, the contrast ratioimprovement layer 100 is a film in which the high refractive index resinlayer 110 adjoins the low refractive index resin layer 120 without theadhesive layer or the bonding layer interposed therebetween. Accordingto this embodiment, the optical film including the contrast ratioimprovement layer 100 can simultaneously improve relative brightness ata front side, can improve both front contrast ratio and side contrastratio by minimizing reduction in the front contrast ratio whileincreasing the side contrast ratio, can reduce a difference between thefront contrast ratio and the side contrast ratio, and can increasecontrast ratio at the same side viewing angle and at the same frontviewing angle, when mounted on a prism sheet having prisms formed on alight exit plane thereof in the liquid crystal display. Particularly,according to this embodiment, the optical film including the contrastratio improvement layer 100 can improve relative brightness at the frontside of the liquid crystal display and can improve the front contrastratio, when mounted on an inverted prism sheet having prisms formed on alight incidence plane thereof in the liquid crystal display, as in thecase of being mounted on the prism sheet having prisms formed on thelight exit plane thereof. The contrast ratio improvement layer 100 mayhave a thickness of about 10 μm to about 100 μm, specifically about 20μm to about 60 μm, more specifically about 20 μm to about 45 μm. Withinthis thickness range, the contrast ratio improvement layer 100 can besufficiently supported by the base layer and can be used in an opticaldisplay.

The high refractive index resin layer 110 may be formed on the baselayer 200 so as to increase light diffusing effects by diffusing lightreaching the low refractive index resin layer 120 in the opticaldisplay. The high refractive index resin layer 110 is directly formed onthe base layer 200. Herein, the expression “directly formed on” meansthat intervening layers such as an adhesive layer, a bonding layerand/or other optical layers are not formed between the high refractiveindex resin layer 110 and the base layer 200. FIG. 1 shows the structurewherein the low refractive index resin layer 120, the high refractiveindex resin layer 110 and the base layer 200 are sequentially stackedone above another. Alternatively, the base layer 200, the low refractiveindex resin layer 120, and the high refractive index resin layer 110 maybe sequentially stacked one above another such that the base layer 200directly adjoins the low refractive index resin layer 120 and light istransmitted through the low refractive index resin layer and the highrefractive index resin layer after passing through the base layer so asto provide advantageous effects of the present invention.

The high refractive index resin layer 110 has a higher refractive indexthan the low refractive index resin layer 120. Specifically, adifference in refractive index between the high refractive index resinlayer 110 and the low refractive index resin layer 120 may be about 0.20or less, specifically about 0.10 to about 0.20, more specifically about0.10 to about 0.15. Within this range of difference in refractive index,the optical film can achieve significant improvement in diffusion oflight and contrast ratio. Particularly, with a difference in refractiveindex in the range of about 0.10 to about 0.15, the optical film canprovide good effects in diffusion of polarized light in the opticaldisplay, thereby improving brightness at the same viewing angle. Thehigh refractive index resin layer 110 may have a refractive index ofabout 1.50 or more, specifically about 1.50 to about 1.70. Within thisrange of refractive index, the optical film can provide good lightdiffusing effects. The high refractive index resin layer 110 may beformed of a UV-curable composition or a thermosetting compositionincluding at least one of a (meth)acrylic resin, a polycarbonate resin,a silicone resin, and an epoxy resin, without being limited thereto.

The high refractive index resin layer 110 includes the patterned portioncomposed of one or more engraved patterns 111 and a flat portion 112formed between the engraved patterns 111. The patterned portion may havea P/W value of greater than about 1 to about 10 or less (P is the cycleof the patterned portion (unit: μm) and W is the maximum width of theengraved pattern (unit: μm)) and the engraved patterns 111 may have abase angle (θ) of 75° to about 90°. The base angle (θ) means an anglebetween an inclined plane 113 of the engraved patterns 111 and animaginary line extending from the maximum width W of the engravedpatterns 111 and may be in the range of 75° to about 90°. Within theseranges of P/W value and base angle, the optical film can improverelative brightness at the front side, can simultaneously improve boththe front contrast ratio and the side contrast ratio, can reduce adifference between the front contrast ratio and the side contrast ratio,and can increase contrast ratio at the same side viewing angle and atthe same front viewing angle, when mounted on the prism sheet havingprisms formed on the light exit plane thereof in the liquid crystaldisplay. In addition, the optical film can improve relative brightnessat the front side and can improve the front contrast ratio, when mountedon the inverted prism sheet having prisms formed on the light incidenceplane thereof in the liquid crystal display, as in the case of beingmounted on the prism sheet having prisms formed on the light exit planethereof. Specifically, the base angle (θ) may range from about 80° toabout 90° and the P/W value may range from about 1.2 to about 8, morespecifically from about 1.3 to about 7.5.

Although FIG. 1 shows the structure wherein the engraved pattern has thesame base angle at both sides thereof, the engraved pattern according tothe present invention may have different base angles so long as the baseangle ranges from 75° to about 90°.

The flat portion 112 can diffuse light and maintain the front contrastratio and brightness by allowing the light reaching the flat portion 112to exit the optical film therethrough. A ratio (W/B) of the maximumwidth W of the engraved pattern 111 to the width B of the flat portion112 may be about 9 or less, specifically about 0.1 to about 5, morespecifically about 0.15 to about 3. Within this range, the optical filmcan improve relative brightness at the front side of the liquid crystaldisplay, can reduce the difference between the front contrast ratio andthe side contrast ratio, and can increase contrast ratio at the sameside viewing angle and the same front viewing angle. Furthermore, theoptical film can prevent the Moiré phenomenon. The flat portion 112 mayhave a width of about 1 μm to about 300 μm, specifically about 3 μm toabout 50 μm. Within this width range, the optical film including theflat portion can improve front brightness.

The engraved pattern 111 may be an engraved optical pattern composed ofa first surface 114 formed at a top part thereof and one or moreinclined planes 113 connected to the first face 114. The first surface114 is formed at the top part of the engraved pattern 111 so as to allowlight reaching the low refractive index resin layer 120 in the opticaldisplay to be further diffused by the first surface 114, therebyimproving viewing angle and brightness. Accordingly, the optical filmaccording to this embodiment can minimize brightness loss throughimprovement in light diffusing effect. Although FIG. 1 shows thestructure wherein the first surface 114 is a flat surface and isparallel to the flat portion 112, the first surface 114 may have fineroughness or a curved surface. In the structure wherein the firstsurface has a curved surface, the engraved pattern 111 may be realizedas a lenticular lens pattern. The first surface 114 may have a width Aof about 0.5 μm to about 30 μm, specifically about 2 μm to about 20 μm.Referring to FIG. 1, the engraved pattern 111 may have a trapezoidalcross-sectional shape in which the first surface is formed at the toppart thereof and the inclined planes are flat surfaces (for example: atruncated prism pattern having a truncated triangular cross-section,that is, a truncated prism or cut-prism shape). Alternatively, theengraved pattern may have a shape in which the first surface is formedat the top part and the inclined plane is a curved surface (for example:a truncated lenticular lens such as cut-lenticular lens pattern, or atruncated micro-lens such as cut-micro lens pattern).

The engraved patterns 111 may have an aspect ratio of about 0.3 to about3.0, specifically about 0.4 to about 2.5, more specifically about 0.4 toabout 1.5. Within this range of aspect ratio, the optical film canimprove the side contrast ratio and viewing angle of the opticaldisplay. The engraved patterns 111 may have a height H of about 40 μm orless, specifically about 30 μm or less, more specifically about 5 μm toabout 15 μm. Within this height range, the engraved pattern can improvecontrast ratio, viewing angle, and brightness without causing the Moiréphenomenon. The engraved pattern 111 may have a maximum width W of about80 μm or less, specifically about 50 μm or less, more specifically about5 μm to about 20 μm or about 10 μm to about 30 μm. Within this widthrange, the engraved pattern can improve contrast ratio, viewing angle,and brightness without causing the Moiré phenomenon.

The patterned portion may have a cycle P of about 5 μm to about 500 μm,specifically about 10 μm to about 50 μm. Within this cyclerange, thepatterned portion can improve brightness and contrast ratio withoutcausing the Moiré phenomenon.

The low refractive index resin layer 120 can diffuse light by refractingthe light incidented through a lower surface of the optical display invarious directions depending upon incident positions of the light. Thelow refractive index resin layer 120 may directly adjoin the highrefractive index resin layer 110. The low refractive index resin layer120 may include a plane facing the high refractive index resin layer 110and one or more filling patterns 121. The filling patterns 121 may atleast partially fill the engraved patterns 111. Herein, the expression“at least partially fill” includes both a structure wherein the engravedpattern is completely filled with the filling pattern and a structurewherein the engraved pattern is partially filled therewith. In thestructure wherein the engraved pattern is partially filled with thefilling pattern, a remaining portion of the engraved pattern may befilled with air or a resin having a predetermined refractive index.Specifically, the resin may have a refractive index which is the same asor higher than that of the low refractive index resin layer and is thesame as or lower than that of the high refractive index resin layer.Although not shown in FIG. 1, the filling pattern and the engravedpattern may extend in a stripe shape, or may be formed in a dot shape.Herein, the term “dot” means that combinations of the filling patternsand the engraved patterns are dispersed.

The low refractive index resin layer 120 may have a refractive index ofless than about 1.52, specifically about 1.35 to less than about 1.50.Within this range of refractive index, the optical film can secure ahigh light diffusing effect and can be easily produced whilesignificantly improving diffusion of polarized light and contrast ratio.The low refractive index resin layer 120 may be formed of a UV-curableor thermosetting composition including a transparent resin.Specifically, the transparent resin may include at least one of a(meth)acrylic resin, a polycarbonate resin, a silicone resin, and anepoxy resin, without being limited thereto. The transparent resin mayhave a light transmittance of about 90% or higher after curing. The lowrefractive index resin layer 120 may be formed of a non-adhesive resinor may be formed of an inherently adhesive resin exhibiting inherentadhesion so as to facilitate interlayer coupling or so as to eliminatean adhesive/bonding layer upon interlayer coupling, thereby reducing thethickness of the optical film for improving contrast ratio. Examples ofthe inherently adhesive resin may include an acrylic resin, an epoxyresin, and a urethane resin.

Although not shown in FIG. 1, at least one of the low refractive indexresin layer and the high refractive index resin layer may furtherinclude a light diffusing agent. The light diffusing agent can furtherimprove the light diffusing effect of the optical film. The lightdiffusing agent may include one or more of an organic light diffusingagent, an inorganic light diffusing agent, or an organic-inorganichybrid diffusing agent.

The base layer 200 is formed on the contrast ratio improvement layer 100to protect the contrast ratio improvement layer 100 while supporting thecontrast improvement layer 100. The base layer 200 is a light passinglayer and allows light having passed through the contrast ratioimprovement layer 100 to pass therethrough.

The base layer 200 may be integrated with the contrast ratio improvementlayer 100. Herein, the term “integrated” means a structure wherein thebase layer and the contrast ratio improvement layer are notindependently separated from each other. The base layer 200 may be aretardation film providing a certain range of retardation or anisotropic optical film. In one embodiment, the base layer may have anin-plane retardation Re of about 8,000 nm or more, specifically about10,000 nm or more, more specifically higher than about 10,000 nm, stillmore specifically about 10,100 nm to about 15,000 nm. Within this range,the base layer can prevent generation of rainbow spots and can improvethe effect of diffusing light having passed through the contrast ratioimprovement layer. In other embodiments, the base layer 200 may have anin-plane retardation Re of about 60 nm or less, specifically about 0 nmto about 60 nm, more specifically about 40 nm to about 60 nm, therebyproviding an isotropic optical film. Within this range of in-planeretardation, the base layer can provide good image quality throughcompensation for viewing angle. Herein, the term “isotropic opticalfilm” means a film having substantially the same nx, ny and nz. Herein,the expression “substantially the same” include not only the case wherenx, ny and nz are completely the same, but also the case where there isan acceptable margin of error between nx, ny and nz.

The base layer 200 may have a thickness of about 30 μm to about 120 μm,specifically about 55 μm to about 105 μm. Within this thickness range,the optical film including the base layer can be used in an opticaldisplay. The base layer 200 may have a light transmittance of about 80%or more, specifically about 85% to about 95%, in the wavelength band ofvisible light. The base layer 200 may include a film obtained byuniaxially or biaxially stretching an optically transparent resin film.Specifically, the resin may include at least one of polyesters includingpolyethylene terephthalate (PET), polybutylene terephthalate,polyethylene naphthalate, and polybutylene naphthalate, cellulose estersincluding acryl resins, cyclic olefin polymer (COP) resins andtriacetylcellulose (TAC), polyvinyl acetate, polyvinyl chloride (PVC),polynorbornene, polycarbonate (PC), polyamide, polyacetal, polyphenyleneether, polyphenylene sulfide, polysulfone, polyether sulfone,polyacrylate, and polyimide. The base layer 200 may include a filmproduced through modification of at least one resin selected from amongthese resins. Modification may include copolymerization, branching,crosslinking, or modification of molecular terminals.

Although not shown in FIG. 1, the base layer may include a base film anda primer layer formed on at least one surface of the base film. The basefilm supports the base layer and may have refractive index ratio in apredetermined range with respect to the primer layer, thereby improvingtransmittance of the base layer. Specifically, a refractive index ratioof the primer layer to the base film (refractive index of the primerlayer/refractive index of the base film) may be about 1.0 or less,specifically about 0.6 to about 1.0, more specifically about 0.69 toabout 0.95, still more specifically about 0.7 to about 0.9, still morespecifically about 0.72 to about 0.88. Within this range, the base filmcan improve transmittance of the base layer. The base film may have arefractive index of about 1.3 to about 1.7, specifically about 1.4 toabout 1.6. Within this range, the base film can be applied to the baselayer, can facilitate regulation of the refractive index with respect tothe primer layer, and can improve transmittance of the base layer. Thebase film may be formed of the resins described above. The primer layeris formed between the base film and the high refractive index resinlayer, and can reinforce adhesion between the base film and the highrefractive index resin layer. The primer layer may have a refractiveindex of about 1.0 to about 1.6, specifically about 1.1 to about 1.6,more specifically about 1.1 to about 1.5. Within this range ofrefractive index, the primer layer can be used in the optical film andexhibit a suitable refractive index with respect to the refractive indexof the base film, thereby improving transmittance of the base layer. Theprimer layer may have a thickness of about 1 nm to about 200 nm,specifically about 60 nm to about 200 nm. Within this thickness range,the primer layer can be used in the optical film and can exhibit asuitable refractive index with respect to the refractive index of thebase film, thereby improving transmittance of the base layer withoutsuffering from brittleness. The primer layer may be a non-urethaneprimer layer free from a urethane group. Specifically, the primer layermay be formed of a composition for the primer layer including resins,such as a polyester resin and an acryl resin, or monomers. The primerlayer can secure the above refractive index by adjusting a mixing ratioof these monomers (for example: molar ratio). The composition for theprimer layer may further include at least one additive such as a UVabsorbent, an antistatic agent, an antifoaming agent, a surfactant, andthe like.

Although not shown in FIG. 1, the optical film may further include afunctional layer on the other surface of the base layer 200. Thefunctional layer may be formed as a discrete layer or may be integrallyformed with the base layer. The functional layer can provide at leastone of anti-reflection, low reflection, hard coating, anti-glare,anti-fingerprint, anti-contamination, diffusion and refractionfunctions.

The optical film for improving contrast ratio 10 may have a lighttransmittance of about 80% or more, specifically about 85% to about 95%,in the wavelength band of visible light (for example: wavelength 380 nmto 780 nm). The optical film for improving contrast ratio 10 may have athickness of about 50 μm to about 200 μm. Within this range, the opticalfilm can secure the light diffusing effect.

Next, an optical film according to another embodiment of the presentinvention will be described with reference to FIG. 2. FIG. 2 is across-sectional view of an optical film according to another embodimentof the present invention.

Referring to FIG. 2, an optical film 20 according to this embodiment issubstantially the same as the optical film 10 according to the aboveembodiment except further including an adhesive/bonding layer 250 on alower surface of the contrast improvement layer 100.

The adhesive/bonding layer 250 is formed on the lower surface of thecontrast ratio improvement layer 100 to attach the optical film forimproving contrast ratio 20 to an optical device such as a polarizingplate. With this structure, the adhesive/bonding layer 250 allowsinternal light to enter the low refractive index resin layer beforetraveling towards the patterned portion of the high refractive indexresin layer in the optical display. The adhesive/bonding layer 250 mayinclude an adhesive layer, a bonding layer, or a combination stackedthereof. The adhesive/bonding layer 250 may be formed of a typicalbonding agent known to those skilled in the art. For example, thebonding layer may include a thermosetting bonding agent or a lightcurable bonding agent. Specifically, the bonding layer may include a(meth)acrylic compound, an epoxy compound, a cyanoacrylate compound, anisocyanate compound, and the like. The adhesive layer may be formed of apressure-sensitive adhesive including a (meth)acrylic adhesive resin, anepoxy resin, a urethane resin, and the like.

Next, an optical film according to a further embodiment of the presentinvention will be described with reference to FIG. 3. FIG. 3 is across-sectional view of an optical film according to a furtherembodiment of the present invention.

Referring to FIG. 3, an optical film 30 according to this embodiment issubstantially the same as the optical film 10 according to the aboveembodiment except that the optical film 30 includes a contrast ratioimprovement layer 100 a, which includes a high refractive index resinlayer 110 a having a curved surface at an interface between an engravedpattern 111 a and a flat portion 112 a, and a low refractive index resinlayer 120 a. In the structure wherein the curved surface is formed atthe interface between the engraved pattern 111 a and the flat portion112 a, an angle between a flat portion of an inclined plane of theengraved pattern and the maximum width of the engraved pattern isdefined as the base angle θ of the engraved pattern 111 a.

Next, an optical film for improving contrast ratio according to yetanother embodiment of the present invention will be described withreference to FIG. 4. FIG. 4 is a cross-sectional view of an optical filmfor improving contrast ratio according to yet another embodiment of thepresent invention.

Referring to FIG. 4, an optical film 40 for improving contrast ratioaccording to this embodiment is substantially the same as the opticalfilm 10 according to the above embodiment except that the optical film40 includes a contrast improvement layer 100 b, which includes a highrefractive index resin layer 110 b including engraved patterns 111 b,inclined planes of which are curved surfaces, and a low refractive indexresin layer 120 b. The structure of the engraved patterns including thecurved surfaces can provide an effect of preventing rapid change inbrightness. Although FIG. 4 shows the engraved pattern having atruncated lenticular lens (cut-lenticular lens) pattern, an inclinedplane of which is a convexly curved surface, it should be understoodthat the present invention is not limited thereto. An angle between atangential line I at a point corresponding to half (H) the height of theengraved pattern and the maximum width of the engraved pattern isdefined as the base angle θ of the engraved pattern, which ranges from75° to about 90°.

A polarizing plate according to the present invention may include theoptical film for improving contrast ratio according to the aboveembodiments of the present invention.

Next, a polarizing plate according to one embodiment of the presentinvention will be described. FIG. 5 is a cross-sectional view of apolarizing plate according to one embodiment of the present invention.

Referring to FIG. 5, a polarizing plate 50 according to this embodimentincludes a first protective layer 300, a polarizer 400, a secondprotective layer 500, an adhesive/bonding layer 250, and an optical filmfor improving contrast ratio, wherein the optical film for improvingcontrast ratio may include the contrast improvement layer 100 and thebase layer 200 according to the present invention. In the structurewherein the polarizing plate includes the optical film for improvingcontrast ratio, polarized light having passed through the polarizer isdiffused while sequentially passing through the low refractive indexresin layer and the high refractive index resin layer, thereby improvingthe front contrast ratio and the side contrast ratio, reducing adifference between the front contrast ratio and the side contrast ratio,and improving contrast ratio at the same side viewing angle and the samefront viewing angle. The polarizing plate 50 may have a thickness ofabout 150 μm to about 400 μm. Within this thickness range, thepolarizing plate can be used in an optical display.

The first protective layer 300 can protect the polarizer 400 whileincreasing mechanical strength of the polarizing plate 50. The firstprotective layer 300 may have a total transmittance of about 90% ormore, specifically about 90% to about 100%, in the wavelength band ofvisible light.

The first protective layer may be an isotropic film. The isotropic filmmay have an in-plane retardation Re of about 60 nm or less, for example,about 0 nm to about 60 nm. Alternatively, the first protective layer maybe a retardation film. The retardation film may have in-planeretardation Re of about 100 nm to about 220 nm, more specifically about100 nm to about 180 nm, and may be, for example, a λ/4 retardation film(that is, a quarter-wave plate, QWP). The retardation film may have anin-plane retardation Re of about 225 nm to about 350 nm, specificallyabout 225 nm to about 300 nm, and may be, for example, a λ/2 retardationfilm (that is, a half wave plate, HWP).

The first protective layer 300 may include at least one of an opticallytransparent protective film and an optically transparent protectivecoating layer.

In the structure wherein the first protective layer is realized by theprotective film, the protective film may be formed of an opticallytransparent resin. The protective film may be produced through meltextrusion of the resin. The protective film may be subjected tostretching, as needed. The resin may include at least one of celluloseester resins such as triacetylcellulose, cyclic polyolefin resins suchas an amorphous cyclic olefin polymer (COP), polycarbonate resins,polyester resins such as polyethylene terephthalate (PET),polyethersulfone resins, polysulfone resins, polyamide resins, polyimideresins, non-cyclic polyolefin resins, polyacrylate resins such aspoly(methyl) methacrylate, polyvinyl alcohol resins, polyvinyl chlorideresins, and polyvinylidene resins. The protective film may be anoptically transparent liquid crystal film.

In the structure wherein the first protective layer is realized by theprotective coating layer, the protective coating layer can secure goodproperties in terms of adhesion to the polarizer, transparency,mechanical strength, thermal stability, moisture blocking performance,and durability. In one embodiment, the protective coating layer may beformed of an active-energy ray curable resin composition, which includesan active-energy ray curable compound and an an initiator. Theactive-energy ray curable compound may include at least one of cationpolymerizable curable compounds, radical polymerizable curablecompounds, urethane resins, and silicone resins. The cationpolymerizable curable compounds may include at least one of an epoxycompound containing at least one epoxy group therein and an oxetanecompound containing at least one oxetane ring therein. The radicalpolymerizable curable compound may be a (meth)acrylic compound having atleast one (meth)acryloyloxy group therein. The epoxy compound mayinclude at least one among hydrogenated epoxy compounds, aliphatic epoxycompounds, alicyclic epoxy compounds, and aromatic epoxy compounds. Theradical polymerizable curable compound can realize a protective coatinglayer that exhibits excellent properties in terms of hardness,mechanical strength and durability. The radical polymerizable curablecompound may be obtained by reacting a (meth)acrylate monomer having atleast one (meth)acryloyloxy group with two or more types of functionalgroup-containing compounds, and may include a (meth)acrylate oligomerwhich has at least two (meth)acryloyloxy groups therein. Examples of the(meth)acrylate monomer include a monofunctional (meth)acrylate monomerhaving a single (meth)acryloyloxy group, a bifunctional (meth)acrylatemonomer having two (meth)acryloyloxy groups, and a polyfunctional(meth)acrylate monomer having three or more (meth)acryloyloxy groups.The (meth)acrylate oligomer may include a urethane (meth)acrylateoligomer, a polyester (meth)acrylate oligomer, an epoxy (meth)acrylateoligomer, and the like. The initiator can cure the active-energy raycurable composition. The initiator may include at least one of aphoto-cationic polymerization initiator and a photosensitizer.

As the photo-cationic polymerization initiator, any typicalphoto-cationic polymerization initiator known in the art may be usedwithout limitation. Specifically, the photo-cationic polymerizationinitiator may include an onium salt containing a cation and an anion.Examples of the cation may include: diaryliodonium such asdiphenyliodonium, 4-methoxydiphenyliodonium,bis(4-methylphenyl)iodonium, bis(4-tert-butylphenyl)iodonium,bis(dodecylphenyl)iodonium and(4-methylphenyl)[(4-(2-methylpropyl)phenyl)iodonium; triarylsulfoniumsuch as triphenylsulfonium and diphenyl-4-thiophenoxyphenylsulfonium;bis[4-(diphenylsulfonio)-phenyl]sulfide; and the like. Examples of theanion may include hexafluorophosphate, tetrafluoroborate,hexafluoroantimonate, hexafluoroarsenate, hexachloroantimonate, and thelike. As the photosensitizer, any typical photosensitizer known in theart may be used without limitation. Specifically, the photosensitizermay include at least one of thioxanthone, phosphorus, triazine,acetophenone, benzophenone, benzoin, and oxime photosensitizer. Theinitiator may be present in an amount of about 0.01 parts by weight toabout 10 parts by weight based on 100 parts by weight of the activeenergy ray-curable compound. Within this range, the initiator can securesufficient curing of the composition to provide high mechanical strengthand good adhesion to the polarizer. The active energy ray-curable resincomposition may further include typical additives such as a siliconeleveling agent, a UV absorbent, an antistatic agent, and the like. Theadditives may be present in an amount of 0.01 parts by weight to about 1part by weight based on 100 parts by weight of the active energyray-curable compound. The protective coating layer may be a liquidcrystal coating layer.

The first protective layer 300 may have a thickness of about 5 μm toabout 200 μm, specifically about 30 μm to about 120 μm. The firstprotective layer may have a thickness of about 50 μm to about 100 μmwhen realized by the protective film and a thickness of about 5 μm toabout 50 μm when realized by the protective coating layer. Within thisthickness range, the first protective layer can be used in a lightemitting display.

Although not shown in FIG. 5, the aforementioned functional layer may befurther formed on an upper surface of the first protective layer. Inaddition, although not shown in FIG. 5, in the structure wherein thefirst protective layer is realized by the protective film, a bondinglayer may be further formed between the first protective layer and thepolarizer. The bonding layer may be formed of a typical bonding agentfor polarizing plates, for example, a water-based bonding agent, aphotocurable bonding agent, and a pressure sensitive bonding agent.

The polarizer 400 is formed on the first protective layer 300 and canpolarize incident light and may include a typical polarizer known tothose skilled in the art. Specifically, the polarizer may include apolyvinyl alcohol-based polarizer produced by uniaxially stretching apolyvinyl alcohol-based film, or a polyene-based polarizer produced bydehydration of the polyvinyl alcohol-based film. The polarizer 400 mayhave a thickness of about 5 μm to about 40 μm. Within this range, thepolarizer can be used in an optical display.

The second protective layer 500 is formed on the polarizer 400 and canprotect the polarizer while improving mechanical strength of thepolarizing plate. The second protective layer may include at least oneof a protective film and a protective coating layer as described in thefirst protective layer, and may have the same or different features interms of thickness, material and retardation from the first protectivelayer 300. Although FIG. 5 shows the polarizing plate including thesecond protective layer 500, a polarizing plate according to anotherembodiment can eliminate the second protective layer in the structurewherein the low refractive index resin layer 120 is formed of thethermosetting composition or the UV-curable composition according to thecomposition thereof. As shown in FIG. 6, a polarizing plate 60 accordingto this embodiment may include a first protective layer 300, a polarizer400, an adhesive/bonding layer 250, a contrast ratio improvement layer100, and a base layer 200, which are sequentially stacked in this order.In a polarizing plate 70 according to a further embodiment wherein thelow refractive index resin layer 120 is formed of the inherent adhesiveresin, a polarizer 400 directly adjoins a contrast ratio improvementlayer 100 such that a first protective layer 300, the polarizer 400, thecontrast ratio improvement layer 100, and a base layer 200 aresequentially stacked in this order, as shown in FIG. 7.

The adhesive/bonding layer 250 may be interposed between the secondprotective layer 500 and the low refractive index resin layer so as tomaintain adhesion between the second protective layer 500 and thecontrast ratio improvement layer 100. The adhesive/bonding layer is thesame as described above. In the structure wherein the contrast ratioimprovement layer 100 includes the low refractive index resin layerexhibiting inherent adhesion as described above, the adhesive/bondinglayer can be omitted. According to this embodiment, a polarizing plate80 includes a first protective layer 300, a polarizer 400, a secondprotective layer 500, a contrast ratio improvement layer 100, and a baselayer 200, which are sequentially stacked in this order such that thesecond protective layer 500 directly adjoins the contrast ratioimprovement layer 100, as shown in FIG. 8.

A liquid crystal display according to the present invention may includethe optical film for improving contrast ratio according to the presentinvention or the polarizing plate according to the present invention. Inone embodiment, the liquid crystal display may include a backlight unit,a first polarizing plate, a liquid crystal panel, and a secondpolarizing plate, which are sequentially stacked in this order, whereinthe second polarizing plate includes the polarizing plate according tothe present invention. The liquid crystal panel includes a firstsubstrate, a second substrate, and a liquid crystal layer securedbetween the first substrate and the second substrate and acting as adisplay medium. The first substrate may include a color filter and ablack matrix mounted thereon. The second substrate may include aswitching device configured to control electro-optical characteristicsof liquid crystals, an injection line configured to supply gate signalsto the switching device and a signal line in order to provide a sourcesignal, a pixel electrode, and a counter electrode. The liquid crystallayer may include liquid crystals evenly aligned upon application of noelectric field. Specifically, the liquid crystal panel may adopt avertical alignment (VA) mode, an IPS mode, a patterned verticalalignment (PVA) mode, or a super-patterned vertical alignment (S-PVA)mode, without being limited thereto.

Next, a liquid crystal display according to one embodiment of thepresent invention will be described with reference to FIG. 9. FIG. 9 isa perspective view of a liquid crystal display according to oneembodiment of the present invention.

Referring to FIG. 9, a liquid crystal display 90 according to thisembodiment includes a light source 650, a light guide plate 600, a prismsheet 700, a first polarizing plate 900, a liquid crystal panel 800, anda second polarizing plate 950, wherein the second polarizing plate 950may include the optical film for improving contrast ratio according tothe embodiments of the present invention. The liquid crystal displayaccording to this embodiment includes the optical film for improvingcontrast ratio, thereby improving both relative brightness and frontcontrast ratio even in the structure wherein the liquid crystal displayincludes the prism sheet 700.

The prism sheet 700 is disposed on the light guide plate 600 and cancollect light received from a light exit plane of the light guide plate600. The prism sheet 700 includes a first light incidence plane facingthe light guide plate 600, a first light exit plane facing the firstlight incidence plane, and one or more prisms formed on the first lightincidence plane so as to provide an inverted prism sheet structure.

Next, the prism sheet according to this embodiment will be describedwith reference to FIG. 10.

Referring to FIG. 10, the prism sheet 700 according to this embodimentmay include a base film 701 and a prism portion 703. An upper surface ofthe base film 701 constitutes the first light exit plane and the prismportion 703 constitutes the first light incidence plane. The prismportion is formed on the first light incidence plane, thereby improvingefficiency in collection and diffusion of light even in the structurewherein the liquid crystal display includes an edge type light source,as in FIG. 10.

The base film 701 supports the prism sheet 700 and may have a thicknessof about 50 μm to about 250 μm, specifically about 100 μm to about 200μm, without being limited thereto. Within this range, the base film canbe used in the liquid crystal display. The base film 701 may be formedof a transparent compound including a transparent thermoplastic resin ora composition including the same. Specifically, the thermoplastic resinmay include at least one of polyester resins such as polyethyleneterephthalate and polyethylene naphthalate, polyacetal resins, acrylicresins, polycarbonate resins, styrene resins, vinyl resins,polyphenylene ether resins, non-cyclic polyolefin resins such aspolyethylene and polypropylene, cyclic olefin resins,acrylonitrile-butadiene-styrene copolymer resins, polyarylsulfoneresins, polyethersulfone resins, polyphenylene sulfide resins,fluorine-based resins, and (meth)acrylic resins. The upper surface ofthe base film 701 constitutes the first light exit plane. Preferably,the first light exit plane is a flat surface on which prisms are notformed.

The prism portion 703 is formed on a lower surface of the base film 701on the light guide plate 600 so as to face the light guide plate 600such that light received from a second light exit plane of the lightguide plate 600 can be directed to the first light exit plane throughthe prism portion 703. An upper surface of the prism portion 703 is aflat surface and is bonded to the lower surface of the base film 701. Alower surface of the prism portion 703 constitutes the first lightincidence plane and has one or more prisms 702 arranged thereon.

The prism portion 703 may include one or more prisms 702 and a valley704 formed between the prisms 702.

The prisms 702 are disposed to face the light guide plate 600 andcollect light received from the light guide plate 600. Light havingpassed through the prisms 702 is diffused through the liquid crystalpanel 800, thereby improving the side contrast ratio, the front contrastratio, and the viewing angle of the liquid crystal display.

The prisms 702 may be an optical pattern having a triangularcross-section.

Although FIG. 10 shows the optical pattern having a triangularcross-section, it should be understood that the present invention is notlimited thereto. The prisms may have a polygonal cross-section, thenumber of sides of which ranges from 4 to 10. Although FIG. 10 shows theoptical pattern of prisms having a sharp top part, the prisms may have arounded top part.

The prism 702 includes two prism planes 702 a, 702 b. Each of the prismplanes 702 a, 702 b is an optically flat surface and one or more of theprism planes 702 a, 702 b may be inclined with respect to a direction L1(in FIG. 10) perpendicular to the first light exit plane. Specifically,an angle 81 defined between the prism plane 702 a and direction L1perpendicular to the first light exit plane may range from about 53° toabout 60°, specifically from about 55° to about 58°. Within this range,the prisms can more efficiently collect light in the front direction ofthe liquid crystal display (the z-axis direction in FIG. 9), therebyimproving the front contrast ratio of the liquid crystal display.

The prisms 702 may have an aspect ratio of about 0.65 to about 0.85,specifically about 0.7 to about 0.8. Within this range of aspect ratio,the prisms can more efficiently collect light in the front direction ofthe liquid crystal display (the z-axis direction in FIG. 9), therebyimproving the front contrast ratio of the liquid crystal display.

The prisms 702 may have a pitch P1 of about 7 μm to about 30 μm,specifically about 10 μm to about 20 μm. The prisms 702 may have aheight H1 of about 4 μm to about 25 μm, specifically about 7 μm to about16 μm. The prisms 702 may have a vertex angle 82 of about 63° to about70°, specifically about 65° to about 68°. Within these ranges of pitch,height and vertex angle, the prisms can more efficiently collect lightin the front direction of the liquid crystal display (the z-axisdirection in FIG. 9), thereby improving the front contrast ratio of theliquid crystal display.

The prisms 702 may be formed of the same or different materials as thebase film 701, or may be formed of a composition including a UV-curableunsaturated compound and an initiator. In one embodiment, the UV-curableunsaturated compound may include epoxy (meth)acrylate, urethane(meth)acrylate, phenylphenol ethoxylated (meth)acrylate,trimethylolpropane ethoxylated (meth)acrylate, fluorene derivativeunsaturated resins, phenoxybenzyl (meth)acrylate, phenylphenoxyethyl(meth)acrylate, ethoxylated thiodiphenyl di(meth)acrylate,phenylthioethyl (meth)acrylate, or oligomers thereof, without beinglimited thereto. The initiator is a photo initiator and may includeketone initiators and phosphine oxide initiators, without being limitedthereto.

The prisms 702 may be arranged in the same direction as a light emittingdirection of the light source 650.

The valley 704 may have a vertex angle 83 of about 63° to about 70°,specifically about 65° to about 68°. With the valley having a vertexangle (θ3) within this range, the prisms can more efficiently collectlight in the front direction of the liquid crystal display (the z-axisdirection in FIG. 9), thereby improving the front contrast ratio.

The liquid crystal panel 800 is disposed between the first polarizingplate 900 and the second polarizing plate 950 so as to allow lightreceived from the first polarizing plate 900 through the prism sheet 700to be directed towards the second polarizing plate 950 therethrough. Theliquid crystal panel 800 has the same structure as described above.

The light guide plate 600 is placed at a side of the light source 650 soas to guide light received from the light source 650 to be directedtowards the prism sheet 700 through internal reflection by the lightguide plate 600.

The light guide plate 600 is configured to allow light to exit therefromat a light exit angle of about 50° to about 90°, specifically about 60°to about 80° without scattering, thereby improving brightness of theliquid crystal display even in the structure wherein the liquid crystaldisplay includes the prism sheet 700. Referring to FIG. 11, the term“light exit angle” means an angle θ defined between a direction L2perpendicular to the light exit plane of the light guide plate 600 (afront side of the liquid crystal display) and a light exit direction,assuming that the direction L2 is 0°.

The light guide plate 600 has a second light incidence plane facing thelight source 650 and a second light exit plane orthogonal to the secondlight incidence plane and facing the prisms 702 of the prism sheet 700.The light guide plate 600 may include a base layer 601, a lenticularlens pattern 602, and a microlens pattern 603. Although FIG. 9 shows thelight guide plate that includes the lenticular lens pattern 602 formedon the second light exit plane and the microlens pattern 603 formed on asurface facing the second light exit plane, it should be understood thepresent invention is not limited thereto.

The base layer 601 may be formed between the lenticular lens pattern 602and the microlens pattern 603 so as to support the lenticular lenspattern 602 and the microlens pattern 603. An upper surface of the baselayer 601 may constitute the second light exit plane, a side surface ofthe base layer 601 may constitute the second light incidence plane, anda lower surface of the base layer 601 may be a light incidence planewhich receives light from the microlens pattern 603. The base layer 601may have a thickness of about 1,000 μm to about 4,000 μm, specificallyabout 2,000 μm to about 3,000 μm. Within this thickness range, the baselayer can be used in an optical display. The base layer 601 may includea film formed of an optically transparent resin. Specifically, the resinmay include at least one of polycarbonate, polymethyl(meth)acrylate(PMMA), polystyrene, and a copolymer resin of methyl methacrylate andstyrene (MS resin).

The lenticular lens pattern 602 is formed on the upper surface of thebase layer 601 so as to guide exit of light received from the base layer601 without scattering the light, thereby improving brightness. AlthoughFIG. 9 shows the light guide plate having the lenticular lens pattern asa first optical pattern, the first optical pattern may include anoptical pattern having a curved surface at a top part thereof. Forexample, the first optical pattern may include a prism pattern having ann-gonal cross-section (n being an integer of 3 to 10), a top part ofwhich has a curved surface. The lenticular lens pattern 602 may have anaspect ratio of about 0.10 to about 0.50 and a radius of curvature ofabout 20 μm to about 200 μm, specifically about 50 μm to about 150 μm.Within these ranges, the lenticular lens pattern can serve to guide anddiffuse incident light, and can reduce viewing angle in the verticaldirection, thereby improving visibility and brightness. The lenticularlens pattern 602 may have a maximum pitch of about 100 μm to about 300μm and a maximum height of about 10 μm to about 150 μm. Within theseranges, the lenticular lens pattern 602 can collect light in the lateraldirection so as to improve light efficiency, can serve to guide anddiffuse incident light, and can reduce viewing angle in the verticaldirection, thereby improving visibility and brightness. The lenticularlens pattern 602 may be formed of the same or different opticallytransparent resin than the base layer 601.

The microlens pattern 603 is formed on the lower surface of the baselayer 601 so as to collect light received from the side surface of thelight guide plate. Although FIG. 9 shows the light guide plate havingthe microlens pattern as a second optical pattern in this embodiment,the second optical pattern may include a prism pattern or a lenticularlens pattern, which has an n-gonal cross-section (n being an integer of3 to 10) in other embodiments. The microlens pattern 603 may have anaspect ratio of about 0.01 to about 0.20, specifically about 0.01 toabout 0.10. Within this range of aspect ratio, the microlens pattern 603can improve efficiency in collection of light received from the lightguide plate. The microlens pattern 603 may have a width of about 100 μmto about 400 μm and a height of about 1 μm to about 50 μm. Within theseranges of width and height of the microlens pattern, the prism sheet canprovide a light collection effect. The microlens pattern 603 may beformed of the same or different optically transparent resin than thebase layer 601.

The base layer 601, the lenticular lens pattern 602, and the microlenspattern 603 may be integrally formed with one another. Herein, theexpression “integrally formed with” means that any bonding layer is notinterposed between the base layer 601, the lenticular lens pattern 602and the microlens pattern 603, and that the base layer 601, thelenticular lens pattern 602 and the microlens pattern 603 are notindependently separated from each other. To this end, the light guideplate 600 may be produced by forming the microlens pattern 603 on onesurface of the base layer 601, which has the lenticular lens pattern 602formed on the other surface thereof through extrusion, by lasermachining or the like. Extrusion and laser machining may be performed bytypical methods in the art.

The light source 650 generates light and may be disposed at one side ofthe light guide plate 600. That is, the light source may be disposed toface the second light incidence plane of the light guide plate 600. Thelight source 650 may be a linear light lamp, a sheet-light lamp, orvarious other light sources such as CCFL or LED. A light source covermay be disposed outside the light source 650 to protect the light source600. Although FIG. 9 shows the light source 650 disposed only on oneside of the light guide plate 600, the light source 650 may also bedisposed on the other side of the light guide plate 600 (opposite theone side of the light guide plate).

The first polarizing plate 900 is disposed between the prism sheet 700and the liquid crystal panel 800 such that the first polarizing plate900 is placed on the prism sheet and under the liquid crystal panel, andcan polarize light received from the prism sheet 700. The firstpolarizing plate 900 may include a polarizer and a first protectivelayer or a second protective layer formed on at least one surface of thepolarizer.

The second polarizing plate 950 is disposed on the liquid crystal panel800 and can polarize and diffuse light received from the liquid crystalpanel 800 through the prism sheet 700. The second polarizing plate 950includes the optical film for improving contrast ratio according to theembodiments of the present invention in order to improve relativebrightness and front contrast ratio. The second polarizing plate 950 mayinclude the polarizing plate according to the embodiment of the presentinvention.

Although not show in FIG. 9, each of the first polarizing plate 900 andthe second polarizing plate 950 may be attached to the liquid crystalpanel 800 via an adhesive/bonding layer. Further, although not shown inFIG. 9, a reflective sheet may be disposed on a lower side of the lightguide plate 600. The reflective sheet can reflect light emitted from thelight source 650 towards the light guide plate 600, thereby improvingluminous efficacy.

Hereinafter, the present invention will be described in more detail withreference to some examples. However, it should be understood that theseexamples are provided for illustration only and are not to be construedin any way as limiting the present invention.

Example 1

A UV-curable resin (SSC-5760, Shin-A T&C) was coated onto one surface ofa PET film (thickness: 80 μm, Re=14,000 nm at a wavelength of 550 nm,Toyobo Co., Ltd.) to form a coating layer. Then, using a film having apatterned portion, which includes embossed patterns having the same baseangles at both sides thereof and a flat portion formed between theembossed patterns, engraved patterns and a flat portion were formed onthe coating layer, followed by curing, thereby forming a high refractiveindex resin layer including a patterned portion, which includes engravedpatterns having the same base angles at both sides thereof as listed inTable 1 (engraved patterns having a trapezoidal cross-section as shownin FIG. 1) and a flat portion formed therebetween. Then, a UV-curableresin (SSC-4560, Shin-A T&C) was coated onto the high refractive indexresin layer such that the engraved pattern could be completely filledwith the UV-curable resin, followed by curing, thereby forming anoptical film for improving contrast ratio, which includes a lowrefractive index resin layer having a filling pattern completely fillingthe engraved patterns.

A polarizer was produced by stretching a polyvinyl alcohol film at 60°C. to three times an initial length thereof and adsorbing iodine to thestretched film, followed by stretching the resulting film to 2.5 timesthe stretched length of the film in an aqueous solution of boric acid at40° C.

A bonding agent for polarizing plates (Z-200, Nippon Goshei Co., Ltd.)was deposited onto both surfaces of the polarizer, followed by bonding aCOP film (ZEON Company) and a PET film (thickness: 80 μm, Toyobo Co.,Ltd.) as first and second protective layers to both surfaces of thepolarizer via the bonding layers, respectively.

An adhesive layer was formed on one surface of the low refractive indexresin layer of the optical film for improving contrast ratio bydepositing an acrylic resin adhesive thereon and the PET film providedas the second protective layer was attached to thereto via the adhesivelayer, thereby providing a polarizing plate including the COP film, thebonding layer, the polarizer, the bonding layer, the PET film, theadhesive layer, the low refractive index resin layer, the highrefractive index resin layer, and the PET film sequentially stacked inthis order.

Examples 2 to 3 and 7 to 11

Polarizing plates were produced in the same manner as in Example 1excluding the engraved patterns and the flat portion changed as listedin Table 1.

Example 4

An optical film was produced in the same manner as in Example 1 exceptthat the engraved patterns and the flat portion were changed as listedin Table 1 and the low refractive index resin layer was formed of anacrylic adhesive resin.

A polarizer was produced in the same manner as in Example 1, and abonding agent for polarizing plates (Z-200, Nippon Goshei Co., Ltd.) wasdeposited onto both surfaces of the polarizer, followed by bonding a COPfilm (ZEON Company) and a PET film (thickness: 80 μm, Toyobo Co., Ltd.)as first and second protective layers to both surfaces of the polarizervia the bonding layers, respectively.

The PET film provided as the second protective layer was attached to thelow refractive index resin layer, thereby providing a polarizing plateincluding the COP film, the bonding layer, the polarizer, the bondinglayer, the PET film, the low refractive index resin layer, the highrefractive index resin layer, and the PET film sequentially stacked inthis order.

Example 5

An optical film was produced in the same manner as in Example 1excluding the engraved patterns and the flat portion changed as listedin Table 1.

A polarizer was produced in the same manner as in Example 1, and abonding agent for polarizing plates (Z-200, Nippon Goshei Co., Ltd.) wasdeposited onto one surface of the polarizer, followed by bonding a COPfilm (ZEON Company) as a first protective layer thereto via the bondinglayer. In addition, the bonding agent was deposited onto the othersurface of the polarizer, followed by bonding the low refractive indexresin layer to the other surface of the polarizer via the bonding layer,thereby providing a polarizing plate including the COP film, the bondinglayer, the polarizer, the bonding layer, the low refractive index resinlayer, the high refractive index resin layer, and the PET filmsequentially stacked in this order.

Example 6

An optical film was produced in the same manner as in Example 1 exceptthat the engraved patterns and the flat portion were changed as listedin Table 1 and the low refractive index resin layer was formed of anacrylic adhesive resin.

A polarizer was produced in the same manner as in Example 1, and abonding agent for polarizing plates (Z-200, Nippon Goshei Co., Ltd.) wasdeposited onto one surface of the polarizer, followed by bonding a COPfilm (ZEON Company) as a first protective layer thereto via the bondinglayer. In addition, the low refractive index resin layer was bonded tothe other surface of the polarizer, thereby providing a polarizing plateincluding the COP film, the bonding layer, the polarizer, the lowrefractive index resin layer, the high refractive index resin layer, andthe PET film sequentially stacked in this order.

Comparative Example 1

A polarizing plate was manufactured in the same manner as in Example 1excluding the engraved patterns and the flat portion changed as listedin Table 1.

Reference Example 1

A polarizing plate was manufactured in the same manner as in Example 1except that the optical film for improving contrast ratio was not used.

Liquid crystal display modules were manufactured using the polarizingplates of Examples and Comparative Examples.

Preparative Example 1: Manufacture of Optical Sheet

A composition comprising 35 wt % of epoxy acrylate, 15 wt % of aurethane acrylate oligomer, 36 wt % of ortho-phenylphenol ethoxylatedacrylate, 10 wt % of trimethylolpropane 9-ethoxylated acrylate, and 4 wt% of a photoinitiator was prepared. The composition was coated onto onesurface of a PET film (T910E, thickness: 125 μm, Mitsubishi Co., Ltd.)to form a coating layer. A prism pattern (triangular cross-section,height: 12 μm, pitch: 24 μm, vertex angle: 90°) was transferred from apattern roll having an embossed pattern corresponding to the prismpattern to the coating layer, followed by curing, thereby forming afirst optical sheet having a first prism pattern formed thereon. Thecomposition was coated onto one surface of a PET film (T910E, thickness:125 μm, Mitsubishi Co., Ltd.) to form a coating layer. A prism pattern(triangular cross-section, height: 12 μm, pitch: 24 μm, vertex angle:90°, aspect ratio: 0.5) was transferred from a pattern roll having anembossed pattern corresponding to the prism pattern to the coatinglayer, followed by curing, thereby forming a second optical sheet havinga second prism pattern formed thereon. An optical sheet was manufacturedby stacking the second optical sheet on the first optical sheet suchthat the longitudinal direction of the first prism pattern wasorthogonal to the longitudinal direction of the second prism pattern.

Preparative Example 2: Manufacture of First Polarizing Plate

A first polarizer was produced by stretching a polyvinyl alcohol film at60° C. to three times an initial length thereof and adsorbing iodine tothe stretched film, followed by stretching the resulting film to 2.5times the stretched length of the film in an aqueous solution of boricacid at 40° C. A first polarizing plate was manufactured by bondingtriacetylcellulose films (thickness: 80 μm) to both surfaces of thefirst polarizer via a bonding agent for polarizing plates (Z-200, NipponGoshei Co., Ltd.).

Preparative Example 3: Manufacture of Liquid Crystal Display Module

The composite optical sheet of Preparative Example 1, the firstpolarizing plate of Preparative Example 2, a liquid crystal panel (PVAmode), and the polarizing plates produced in Examples and ComparativeExamples were sequentially assembled, thereby fabricating a liquidcrystal display module.

Schematic configurations of the liquid crystal display modules areprovided in Tables 1 and 2. The liquid crystal display modulesmanufactured in Examples and Comparative Examples were evaluated as tothe following properties, and evaluation results are shown in Tables 1and 2.

(1) Relative brightness: An LED light source, a light guide plate, and aliquid crystal display module were assembled to fabricate a liquidcrystal display including an edge type LED light source at one sidethereof (having the same configuration as a Samsung LED TV (UN32H5500)except for the configuration of the liquid crystal display modulesmanufactured in Examples and Comparative Example 1. Front brightness wasmeasured in a white mode and a black mode in a spherical coordinatesystem (0°, 0°) using an EZ CONTRAST X88RC (EZXL-176R-F422A4, ELDIM Co.,Ltd.). Relative brightness was calculated by {(brightness of Examples orComparative Example 1)/(brightness of Reference Example 1)}×100. Atarget relative brightness value was 90% or more.

(2) Contrast ratio: A liquid crystal display was manufactured in thesame manner as in (1) and contrast ratio was measured in a sphericalcoordinate system (Φ, θ) using an EZ CONTRAST X88RC (EZXL-176R-F422A4,ELDIM Co., Ltd.). A target side contrast ratio was 110 or more and atarget front contrast ratio was 85 or more.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 HighShape of Cut-prism Cut-prism Cut-prism Cut-prism Cut-prism Cut-prismrefractive engraved index pattern resin Width of 7 6 8 7 7 7 layer firstsurface (flat surface) of engraved pattern (μm) Maximum 7 6 8 7 7 7width of engraved pattern (μm, W) Height of 7 7 7 6 8 7 engraved pattern(μm) Width of 7 7 6 7 7 3 flat portion (μm) Cycle 14 14 14 14 14 10 (μm,P) Base 90 90 90 90 90 90 angle of engraved pattern (°) P/W 2 2.33 1.752 2 1.43 Refractive 1.59 1.59 1.59 1.59 1.59 1.59 index Low Refractive1.47 1.47 1.47 1.47 1.47 1.47 refractive index index resin layerRelative brightness 99 99 99 99 99 99 at front side in white mode (%)Relative brightness 99 99 99 99 99 99 at front side in black mode (%)Front contrast ratio 100 100 100 100 100 100 (0°, 0°) Side contrastratio 173 173 170 159 183 158 (0°, 60°)

TABLE 2 Comparative Reference Example Example Example Example ExampleExample Example 7 8 9 10 11 1 1 High Shape of Cut- Cut- Cut- Cut- Cut -Cut-prism — refractive engraved prism prism prism prism lenticular indexpattern resin Width of 5 5 5 5 4.3 4.1 — layer first surface (flatsurface) of engraved pattern (μm) Maximum 7 7 7 7 8.2 7 — width ofengraved pattern (μm, W) Height of 7 7 7 7 7 4 — engraved pattern (μm)Width of 7 15 23 43 5.8 7 — flat portion (μm) Cycle 14 22 30 50 14 14 —(μm, P) Base 82 82 82 82 82 70 — angle of engraved pattern(°) P/W 2 3.144.29 7.14 1.71 2 — Refractive 1.59 1.59 1.59 1.59 1.59 1.59 — index LowRefractive 1.47 1.47 1.47 1.47 1.47 1.47 — refractive index index resinlayer Relative brightness 97 98 98 99 96 82 100 at front side in whitemode (%) Relative brightness 110 106 103 103 112 101 100 at front sidein black mode (%) Front contrast ratio 88 92 95 96 86 81 100 (0°, 0°)Side contrast ratio 161 130 121 112 155 129 100 (0°, 60°)

As shown in Tables 1 and 2, the optical films and the polarizing platesaccording to the present invention could increase relative brightnessand side contrast ratio while minimizing decrease in side contrast ratioand front contrast ratio.

Preparative Example 4: Manufacture of Light Guide Plate

A light guide plate was produced by forming a microlens pattern (width:350 μm, height: 15 μm, aspect ratio: 0.04) on a lower surface of apoly(methyl) methacrylate (PMMA) film (thickness: 3,000 μm), which has alenticular lens pattern (width: 150 μm, height: 34 μm, aspect ratio:0.23, radius of curvature: 100 μm) on an upper surface thereof, by lasermachining.

Preparative Example 5: Manufacture of Prism Sheet

A UV-curable resin (refractive index: 1.55) was coated onto a patternroll having an engraved prism pattern (width: 17 μm, height: 12.6 μm,vertex angle: 68°, triangular cross-section). The coating layer wasbrought into contact with one surface of a polyethylene terephthalate(PET) film (thickness: 125 μm), followed by irradiation with UV light ata dose of 200 mJ, thereby providing a prism sheet having a prism patternon the one surface of the PET film.

Example 12

A polarizing plate was manufactured in the same manner as in Example 1.A liquid crystal display was manufactured by sequentially stacking thelight guide plate of Preparative Example 4, the prism sheet ofPreparative Example 5, the first polarizing plate of Preparative Example2, the liquid crystal panel, and the polarizing plate of Example 1.Here, the lenticular lens pattern of the light guide plate was disposedto face the prism pattern of the prism sheet (the prism sheet ofPreparative Example 5 was an inverted prism sheet). In addition, the COPfilm of the polarizing plate of Example 1 was attached to the liquidcrystal panel.

Example 13

A liquid crystal display was manufactured in the same manner as inExample 12 except that the polarizing plate of Example 7 was usedinstead of the polarizing plate of Example 1.

Example 14

A liquid crystal display was manufactured in the same manner as inExample 12 except that the polarizing plate of Example 8 was usedinstead of the polarizing plate of Example 1.

Example 15

A liquid crystal display was manufactured in the same manner as inExample 12 except that the polarizing plate of Example 11 was usedinstead of the polarizing plate of Example 1.

Comparative Example 2

A liquid crystal display was manufactured in the same manner as inExample 12 except that the polarizing plate of Comparative Example 1 wasused instead of the polarizing plate of Example 1.

Reference Example 2

A liquid crystal display was manufactured in the same manner as inExample 12 except that the polarizing plate of Reference Example 1 wasused instead of the polarizing plate of Example 1.

The liquid crystal displays manufactured in Examples and ComparativeExample were evaluated as to the following properties, and evaluationresults are shown in Table 3.

(1) Relative brightness: An LED light source and each of the liquidcrystal displays of Examples and Comparative Example 2 were assembled tofabricate a liquid crystal display including an edge type LED lightsource at one side thereof (having the same configuration as a SamsungLED TV (UN32H5500) except for the configuration of the liquid crystaldisplay modules of Examples and Comparative Example. Front brightnesswas measured using an EZ CONTRAST X88RC (EZXL-176R-F422A4, ELDIM Co.,Ltd.). Relative brightness was calculated by {(front brightness ofExamples or Comparative Examples)/(front brightness of Reference Example2)}×100.

(2) Percent of contrast ratio: A liquid crystal display was manufacturedin the same manner as in (1) and front contrast ratios were measured ina spherical coordinate system (Φ, θ) using an EZ CONTRAST X88RC(EZXL-176R-F422A4, ELDIM Co., Ltd.). Percent of contrast ratio wascalculated by {(front contrast ratio of Examples or ComparativeExamples)/(front contrast ratio of Reference Example 2)}×100.

TABLE 3 Example Example Example Example Comparative Reference 12 13 1415 Example 2 Example 2 Prism sheet Preparative Preparative PreparativePreparative Preparative Preparative Example 5 Example 5 Example 5Example 5 Example 5 Example 5 Location of prism Light Light Light LightLight Light on prism sheet incidence incidence incidence incidenceincidence incidence plane plane plane plane plane plane Kind ofpolarizing Example 1 Example 7 Example 8 Example 11 ComparativeReference plate Example 1 Example 1 Relative brightness 168 163 170 167141 100 (%) Percent (0°, 0°) 145 134 140 129 123 100 of front contrastratio

As shown in Table 3, the liquid crystal displays of Examples had highrelative brightness and a higher percent of front contrast ratio thanthe liquid crystal display of Comparative Example 2.

It should be understood that various modifications, changes,alterations, and equivalent embodiments can be made by those skilled inthe art without departing from the spirit and scope of the invention.

The invention claimed is:
 1. An optical film for improving contrastratio, comprising: a base layer and a contrast ratio improvement layerformed on the base layer, wherein the contrast ratio improvement layercomprises: a high refractive index resin layer including a patternedportion composed of one or more engraved patterns and a flat portionformed between the engraved patterns; and a low refractive index resinlayer directly formed on the patterned portion, the low refractive indexresin layer includes one or more filling patterns, the engraved patternis completely filled with the filling pattern, and the engraved patternshave an aspect ratio of about 0.3 to about 3.0, the engraved patternshaving a base angle of 75° to about 90°, the patterned portion having aP/W value of greater than about 1 to about 10 or less (P being the cycleof the patterned portion (unit: μm) and W being the maximum width of theengraved pattern (unit: μm)).
 2. The optical film according to claim 1,wherein the patterned portion has a P/W value of about 1.2 to about 8.3. The optical film according to claim 1, wherein the engraved patternscomprise an optical pattern composed of a first surface formed at a toppart thereof and at least one inclined plane connected to the firstsurface, the inclined plane being a flat surface or a curved surface. 4.The optical film according to claim 3, wherein the first surface is aflat surface and is parallel to the flat portion.
 5. The optical filmaccording to claim 1, wherein a difference in refractive index betweenthe high refractive index resin layer and the low refractive index resinlayer ranges from about 0.10 to about 0.15.
 6. The optical filmaccording to claim 1, having a stack structure of the low refractiveindex resin layer, the high refractive index resin layer and the baselayer sequentially stacked in this order, or a stack structure of thebase layer, the low refractive index resin layer and the high refractiveindex resin layer sequentially stacked in this order, wherein the baselayer directly adjoins the high refractive index resin layer or the lowrefractive index resin layer.
 7. The optical film according to claim 1,wherein the base layer has an in-plane retardation Re of about 8,000 nmor more at a wavelength of 550 nm, as represented by Equation A:Re=(nx−ny)×d  <Equation A> (In Equation A, wherein nx and ny arerefractive indexes of the base layer at a wavelength of 550 nm in theslow axis direction and the fast axis direction thereof, respectively,and d is the thickness of the base layer (unit: nm)).
 8. A polarizingplate comprising the optical film for improving contrast ratio accordingto claim
 1. 9. The polarizing plate according to claim 8, comprising: afirst protective layer, a polarizer, a second protective layer, anadhesive/bonding layer, and the optical film for improving contrastratio sequentially stacked in this order.
 10. The polarizing plateaccording to claim 8, comprising: a first protective layer, a polarizer,a second protective layer, and the optical film for improving contrastratio sequentially stacked in this order, wherein the second protectivelayer directly adjoins the optical film for improving contrast ratio.11. The polarizing plate according to claim 10, wherein the lowrefractive index resin layer is formed of an adhesive resin.
 12. Thepolarizing plate according to claim 8, comprising: a first protectivelayer, a polarizer, an adhesive/bonding layer, and the optical film forimproving contrast ratio sequentially stacked in this order.
 13. Thepolarizing plate according to claim 8, comprising: a first protectivelayer, a polarizer, and the optical film for improving contrast ratiosequentially stacked in this order, wherein the polarizer directlyadjoins the optical film for improving contrast ratio.
 14. Thepolarizing plate according to claim 13, wherein low refractive indexresin layer is formed of an adhesive resin.
 15. A liquid crystal displaycomprising the optical film for improving contrast ratio according toclaim
 1. 16. A liquid crystal display comprising: a light guide plate; aprism sheet; a first polarizing plate; a liquid crystal panel; and asecond polarizing plate, wherein the prism sheet comprises one or moreprisms formed on one surface thereof facing the light guide plate, andthe second polarizing plate comprises the optical film for improvingcontrast ratio according to claim
 1. 17. The liquid crystal displayaccording to claim 16, wherein each of the prisms comprises two prismplanes, and at least one of the prism planes has an inclined angle θ1 ofabout 53° to about 60° with respect to a direction perpendicular to alight exit plane of the prism sheet.
 18. The liquid crystal displayaccording to claim 16, wherein each of the prisms has a vertex angle 82of about 63° to about 70°.
 19. The liquid crystal display according toclaim 16, wherein the light guide plate allows light to exit therefromat a light exit angle of about 50° to about 90°.